Motion stages (XY tables and rotary tables) are widely used in various manufacturing, inspection and assembling processes. A common solution currently in use achieves XY motion by stacking two linear stages (i.e. a X-stage and a Y-stage) together via connecting bearings.
A more desirable solution involves having a single moving stage capable of XY motion, eliminating additional bearings. It might also be desirable for such a moving stage to be able to provide at least some Z motion. Attempts have been made to design such displacement devices using the interaction between current-carrying coils and permanent magnets. Examples of efforts in this regard include the following: U.S. Pat. No. 6,003,230; U.S. Pat. No. 6,097,114; U.S. Pat. No. 6,208,045; U.S. Pat. No. 6,441,514; U.S. Pat. No. 6,847,134; U.S. Pat. No. 6,987,335; U.S. Pat. No. 7,436,135; U.S. Pat. No. 7,948,122; US patent publication No. 2008/0203828; W. J. Kim and D. L. Trumper, High-precision magnetic levitation stage for photolithography. Precision Eng. 22 2 (1998), pp. 66-77; D. L. Trumper, et al, “Magnet arrays for synchronous machines”, IEEE Industry Applications Society Annual Meeting, vol. 1, pp. 9-18, 1993; and J. W. Jansen, C. M. M. van Lierop, E. A. Lomonova, A. J. A. Vandenput, “Magnetically Levitated Planar Actuator with Moving Magnets”, IEEE Tran. Ind. App., Vol 44, No 4, 2008.
More recent techniques for implementing displacement devices having a movable stage and a stator are described in:                PCT application No. PCT/CA2012/050751 (published under WO/2013/059934) entitled DISPLACEMENT DEVICES AND METHODS FOR FABRICATION, USE AND CONTROL OF SAME; and        PCT application No. PCT/CA2014/050739 (published under WO/2015/017933) entitled DISPLACEMENT DEVICES AND METHODS AND APPARATUS FOR DETECTING AND ESTIMATING MOTION ASSOCIATED WITH SAME.        
There is a general desire to provide displacement devices having characteristics that improve upon those known in the prior art. One area where there is room for improvement over existing displacement devices is in the controllable movement of multiple (two or more) movable stages in a displacement device (e.g. relative to a single stator). It will be appreciated that there are multiple applications where it may be desirable (e.g. for efficiency or any other reasons) why it might be advantageous to be able to move multiple movable stages in a displacement device. A challenge associated with controllably moving multiple movable stages in a displacement device involves cross-coupling between the forces generated to move the multiple movable stages. For example, forces generated by the displacement device to move a first movable stage may cross-couple into one or more other movable stages. There is a desire to move multiple movable stages in a displacement device.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.